Photographic emulsion



Feb. 23, 1932.. 1.. G. s. BRQOKER 1,846,301

- PHOTOGRAPHIC EMULSION Filed March '12, 1950 Leslie 6. Breaker:

Qwomtom M bm Patented Feb. 23, 1932 UNITED STATES PATENT OFFICE LESLIE G. S. BROOKER, OF ROCHESTER, NEW YORK, ASSIGNOR TO EASTMAN KODAK COMPANY, OF ROCHESTER, NEW YOBJLA. CORPORATION OF NEW YORK PHOTOGRAPHIC EMULSION Application filed March 12, 1930. Serial illo. 435,104.

This invention relates to a new composition of matter and particularly to a new class of photographic sensitizing dyes and a method for their preparation.

It is well known in the photographic art that in order to render photographic emulsions sensitive to substantially all the visible rays of the spectrum, it is necessary to treat the emulsion. either by overcoating or by admixture in the emulsion itself, with a compound which extends the sensitivity of the emulsion beyond its natural sensitivity. An untreated emulsion will generally record only the short waves, such as the blue and violet. By the proper use of a suitable dye,

this restricted sensitivity can be varied at will within certain limits; for example, the emulsion can be rendered strongly sensitive to rays of a particular wave length at the expense of other wave bands or it can be rendered sensitive to all the visual rays in substantially equal proportions.

An object of the present invention is to provide a light-sensitive emulsion, the sensitivity of which is augmented over certain wave bands of the spectrum. Another object of this invention is to provide a light- .-=ensitivc dye to be incorporated in or coat ed upon photographic gelatino-silver-halide emulsions in order to increase their sensitivity. A further object of this invention is to provide a method for the preparation of such dyes. Other objects will hereinafter appear.

In my co-pending application Serial No. 337.177. tiled February 2, 1929, I have described a photo-sensitizing dye. which is a cyanine dye of the thiocarboeyanine series containing naphthalene nuclei. In this dye the three-carbon chain connecting the two of the central carbon atom in the three-carbon chain in the dye derived from 2-methyl-B- naphthothiazole described in my former application.

In the accompanying drawing the color denoting a decrease in intensity of the light ray as it affects the emulsion, the greatest intensity of any wave being at the base line. The cross-hatched area under the stippled band indicates substantially maximum density with substantially no reduced silver above.

the band, a gradual gradation in density extending through the band. The emulsion,

of course, is of maximum density below the curve. It will be noted from this drawing of the spectro sensitometric chart that this particular dye has an exceedingly strong maximum at 660 and continues strong even to 690 This dye also gives an exceptionally uniform sensitivity from 520 to 690 which is an unusual range of high sensitivity.

I will now explain a method for the production of this particular class of dyes, but it will be understood that I am not to-be restricted by the definite proportions or exact ingredients therein given except as they may be so indicated in the claims appended hereto. It will likewise be understood that the chemical structural formulae employed are theoretical and are given so that those skilled in the art may more readily understand the composition of these dyes. Whether or not the chemical structure given is correct, will in no way limit the scope of this lnventlon.

A method for the preparation of the dyes, to-

gether with the suggested equivalents that may be used in such preparations, will enable skilled organic chemists to prepare these dyes no matter what their theoretical structuralformulae may be. The structural formulae given, however, are believed to be correct according to our present knowledge.

The general method for the preparation of this S-methyl dye may be carried out in the followingmanner A 2-methyl beta naphthothiazole is first converted into an alkyl quarternary salt, such as the metho or etho paratoluene sulfonate by heating with a suitable substance at an elevated temperature for a considerable time and this salt is then treat- .ed with 2 molecular proportions of trialkyl ortho acetate in a suflicient-amount of boiling dry pyridine; After several hours boiling, the dye is allowed to crystallize out or may be precipitated by adding to the reaction mixture a salt having a suitable anion, such, for

example, as ammonium bromide; The dye may then be recrystallized to obtain it in a pure form.

Example 1 The 8-methyl 2:2 diethyl 314:3'Z4;.dl-'

benzo thiocarbocyanine bromide may be prepared in the following manner by the three- I step process Step A: One molecular proportion of 2- methyl beta naphthothiazole which may be prepared by well known methods and whica has the following structural formula is condensed with one molecular proportion of ethyl paratoluene sulfonate by heating the substances together at 130 C. for several days. The crude quartcrnary salt is freed from unchanged starting materials by dissolving these out with acetone.

water to the above reaction mixture and the whole is set aside to cool. The crystals which separate are filtered off and washed with suc- 'cessive portions of acetone to remove tarry matters; in methyl alcohol solution they give a reddish-purple solution.

The several reactions involved in the above example are believed to be as follows:

Step A:

CH1 CCH3 S 2-methy1 N beta naphtho- C/ thiazole OOH: 2H5 0S0: etho p-toluene l sulfonate N CzHaSOa ethyl p-toluene sulfonate 2-methyl beta V naphthothiazole Step B:

. Crude j 2 plrgguct CHaC (00 515)? Step A ethyl orthO N acetate C H N, HOSO C7H7 3 C H OH.

Step C:

S-methyl 2:2 diethyl 324:3 :4

dihenzo tliiocarbocyanine bromide.

entirely arbitrary, but the system here em-v ployed is according to current usage. A- dye derived from 2-methyl beta naphthothiazole, for instance, will have the following struc- \N t .0. I

and Will be called 8-alkyl, aryl or aralkyl- 2: 2-dialkyl similar or dissimilar 3: 1:23 :4- dibenzothiocarbocyanine salt, and is obtained by using the ortho-esters of carboxylic acids with these various alkyl or aryl groups directly linked to the carbon atom of the trialkyloxy-methyl group (e. g. trialkyl ortho phenyl acetate, trialkyl ortho propionate, methyl diethyl ortho iso caproate, etc.)

It is, of course, understood that numerous equivalents having the above major nuclei,

may be prepared and in the structure, for ex ample, the R grouping may represent similar or dissimilar alkyl groups while X may rep resent any suitable acid radical that may be used to precipitate the dye, for example, a halide, paratoluene, sulfonate, or alkylo sulfate or, in fact, any suitable acid radical Which will not greatly decrease or destroy the sensitizing properties of the dye, this radical being necessary to give electrical neutrality to the molecule. In the claims the phrasea suitable acid radical-is employed 'to designate this group of acid radicals.

The A position in the above configuration may represent alkyl, aryl, aralkyl or similar groupings. These groupings may be linked to the carbon atom in the 8 position by efi'ect- I Example 2 8 grams (1 mol.) of 2-methyl beta napthathiazole etho-ptoluene sulfonate, 5.4 grams (2 mol.) of trimethyl-ortho-propionate are refluxed with 35 cc. of dry pyridine for approximately one hour. A hot aqueous solution of potassium iodide is added. After allowing this solution to cool, the precipitate is filtered out. The product is digested in hot acetone and again filtered. The dye is then boiled with successive portions of water until tree from the ethiodide of the base. The crude dye obtained in one reaction weighed .36 grams and consisted of a purplish-black powder. Upon crystallization from methyl alcohol minute dark green crystals of the dye were obtained, which give a purplish solution in this solvent. This dye is called 2 2 8- triethyl 3 4 3 4'-dibenzothiocarbocyanine iodide. The structure of this dyeis similar to that give above, the Rs and A being replaced by ethyl groups.

Example 3 7.7 grams (1 mol.) of 2-methyl beta naphthothiazole metho-p-toluene sulfonate, 8.2 grams (2 mol.) of methyl-diethyl-ortho-isocaproate are refluxed for about 45 minutes in 40 cc. of dry pyridine. To the resultant solution 10 grams of potassium iodide dissolved in 50 cc. of hot Water is added to precipitate the dye Which after standing for about 10 to 12hours is filtered, washed with ,boiling water and then warm acetone to remove the impurities. Theproduct Weighs 1.5 grams and is an olive green color. Upon crystallization from methyl alcohol green felted needles are produced. This dye is called 2:2 dimethyl 8 iso-amyl 354:3'z4' di berizo thiocarbocyanine iodide. Its structural formula is similar to that given above except that the Rs are replaced by methyl groups and the A by .an iso-amyl group.

As the preparation of trimethyl-ortho-propiona-te is not described in the literature, I am giving it here. 110 grams of propio nitrile, grams of anhydrousmethyl alcohol and ccs. of anhydrous ethyl ether are chilled to about 5 C. and 80 grams of dry hydrochloric acid gas passed into the mixture.

4 washed with dry. ether and the excess hydrochloric acid removed by drying oyer powdered caustic soda under reduced pressure.

' To the product 420 ccs. of anhydrous methyl trate distilled under reduced pressure.

alcohol are added. The solution is allowed to stand for two days, filtered and the fil- The fraction boiling between 125 to 129 C. is used in the preparation of the dye. The methyl diethyl ortho-iso-carproate is prepared in much the same manner from iso-carpro- 1 5 nitrile.

In the preparation of an emulsion containing these ,photo-sensitizers it has been found that they may be incorporated in the emul sion from their solution in methyl alcohol.

While dyes having good sensitizing power generally require from 5 to 100 milligrams per 100 cc. of the emulsion, the more powerful dyes may require as little as 5 milligrams or less in the same amount to obtain the maxi-- mum sensitizing power of the particular dye used.

From a consideration of the above descriptions, it will be likewise realized that any thio carbocyanine dye in which the 8 position is occupied by an alkyl, aryl or aralkyl group and the 3:4 and 3' :4'positions by fused-on benzene rings, substituted or unsubstituted, and in which the Rs attached to the nitrogen atoms in the thiazole rings' denote similar or dissimilar alkyl groups and X denotes a suitable acid radical will come within the scope of this invention as well as the employment of such dyes as sensitizers in the photographic emulsion.

What Iclaim as newand desire to be secured by Letters Patent of the United States 1. A photographic gelatino-silver-halide emulsion contalning a cyanine dye which contains; two naphthothiazole nuclei linked together by a tri-methenyl chain the hydrogen of the central carbon atom of which has been substituted by an alkyl, aryl or aralkyl group containing more than one carbon atom.

2. A photographic gelatino-silver-halide emulsion containing a cyanine dye which contains-two beta-naphthothiazole nuclei linked together by a tii-me-thenyl chain the hydrogen of the central carbon atom of which has been substituted by an alkyl, aryl or aralkyl 'group. p

3'. A photographic gelatino-silver-halide emulsion containing a cyanine dye which contains two beta-naphthothiazole nuclei linked tains two beta-nap together by a tri-methenyl chain the hydrogen of the central carbon atom of which has been substituted by a methyl group.

5. A photographic gelatino-silver-halide emulsion containin a cyanine dye which confithothiazole nuclei linked together by 'a tri-methen'yl chain the h drogen of the central carbon atom of whic has been substituted b an ethyl group.

6. A photograp ic gelatino-silver-halide emulsion containing an 8-alkyl, arylor aritlkyl-3: 4: 3 dibenzo-thiocarbocyanine sa t.

7. A photogi aphic gelatino-silver-halide emulsion containing an 8-alkyl-3z4z3 :4- dibenzo-thiocarbocyanine salt.

8. A photographic gelatino-silver-halide emulsion containing an 8-methyl-3 4: 3' 4'- dibenzo-thiocarboc anine salt.

9. A photograp ic gelatino-silver-halide emulsion containing an 8-alkyl-3:4=:3 :4- dibenzo-thiocarbocyanine salt, the nitrogen atoms of which are each linked to an alkyl radical while one is linked to radical. i

10. A photographic gelatino silver-halide emulsion containing an 8-alkyl-3:4:3 4- dibenzo-thiocarbocyanine salt, the nitrogen atoms of which are linked to dissimilar alkyl radicals while one is linked to a suitable acid radical.

11. A photographic gelatino-silver-halide emulsion containing an 3-alkyl-3z4z3' 4- dibenzo-thiocarbocyanine sa-1t, the nitrogen atoms of which are each linked to an ethyl group while one is linked to a bromine atom.

12. A photographic gelatino-silver-halide emulsion containing an 8-methyl-2:2-dietiliyl 3: 4: 3' :4 dibenzo thiocarbocyanine sa 13. A photographic gelatino-silver-halide emulsion containing a 2:2z8-triethyl-3z4:

together by a tri-methenyl chain the h 'droen of the central carbon atom of whic has een substituted by an alkyl, aryl or aralkyl oup. Signed at Rochester, New York, this 5th day f March, 1930.

LESLIE G. S. BROOKER.

' tains two beta-naphthothiazole nuclei linked together by a tri-methenyl chain the hydrogen of-the central carbon atom of which has CERTIFICATE OF CORRECTION.

Patent No. 1,846,301. Granted February23, 1932, to

LESLIE c. s. BROOKER.

it is hereby certified that error appears in the printedspecification of the above numbered patent requiring correction as follows: Page 3, line 54, strike out the comma after "paratoluene"; page 4, line 12, for themisspelled compound word "ortho-iso-carproate" read ortho-iso-caproate, and lines 13 and 14, for "isocarpronitrile" read iso-capronitrile; and that the said Letters Patent should be read with these corrections therein that the same may coniorni to the record of the case in the Patent Office.

Signed and sealed this 26thday of April, A. I). 1932.

M. J. Moore,

(Seal) Acting Commissioner'of Patents. 

